The present invention relates to an automatic white balance control device and a video camera with the automatic white balance control device, particularly to an automatic white balance control device and a video camera with a white balance control device which can be controlled at high speed, change white balance control modes corresponding to photograph conditions and operate white balance control stably at a moment when actual recording is started.
In a production operation of an automatic white balance control device for a video camera, in the case that a color temperature is detected from an output signal of an image pick-up elements of a charge coupled device (CCD) and so on, a control signal is detected from a color temperature detecting signal and then gains of amplifiers for controlling white balance control is controlled by feed forward control, control error of white balance caused by dispersion of image pick-up elements, gap of color temperatures between a reference illuminating light memorized in a production operation and natural sunshine or actual illuminating light of various fluorescent lamps can be reduced.
In an automatic white control device according to the present invention, while an iris is moved to open at high speed, a certain value of a white balance control signal can be detected.
Prior Art
In a conventional video camera, white balance is controlled in order to obtain a white reproduced picture image when a white object is photographed. In a white balance control operation, gains of a red singal and a blue signal of the video camera are controlled with reference to a green signal.
In an automatic white balance control circuit in a type of integrating picture image, white balance is controlled in a condition that integrated color signal elements of whole pick-up image would become achromatic color.
In the automatic white balance control circuit in the type of integrating picture image, color signal elements are integrated. There are two types depending on integrating processes. One type is to integrate color signals of a whole picture image totally and another type is to integrate color signals of each divided areas of a picture image.
The type of separately integrating color signals of each area of a picture image will be described with reference to FIG. 1. As shown in FIG. 1, a picture image is divided to a plurality of areas (sections). Usually, each areas are numbered from a1 to a20 in order, for instance. In actuality, there are a large number of divided areas. However, to explain the operation of the invention simply, the number of the divided areas is set to be twenty in FIG. 1. During the first vertical scanning period (herein after it is referred as "V term"), a signal element of an area a1 is integrated and an integrated value i1 is obtained. During the second V term, a signal element of an area a2 is integrated and an integrating value i2 is obtained. Likewise, each areas, areas a3, a4, a5, . . . are successively scanned for every V term in order. Finally, an integrated value i20 of an area a20 can be obtained in the 20th V term. Among the integrated values i1 through i20, the integrated values which indicates white data are selected. A color temperature of an object is detected based on selected data (integrated values) Thus, white balance is controlled. In the above process, areas of which integrated values mean white data are only selected among the whole of areas. The type of separately integrating color signals is superior to the type of totally integrating color signals in view of accuracy.
In an integrated circuit (IC) utilized in a conventional commercially produced video camera, integrating calculation is operated only one time for each V term. In automatic white balance control in the type of separately integrating color signals, it has to wait for a period (V term x number of divided areas) to control white balance once time. Therefore, if color temperature would be changed rapidly, white balance control can not respond to such a change. On the other hand, in the type of totally integrating color signals, a data calculation for white balance control can be operated within one V term.
In a conventional automatic white balance control device for a video camera, there are two kinds depending on control operations. One is a feed back control type and another is a feed forward type.
In an automatic white balance control device of the feed back control type, gains of white balance control amplifiers are controlled to equalize a color temperature detected signal output from an image pick-up element such as a charge coupled device (CCD) and a reference signal. If a controllable range is wide, dispersion of image pick-up elements, i.e. CCD, is adversely influenced to a control result.
In an automatic white balance control device of the feed forward control type, color elements output from an image pick-up element such as a charge coupled device (CCD) are divided into each element color signals and detected values for each elementary color signal R, G, B are integrated for every one field. Further, ratios R/B and B/G are calculated and control values Rcont and Bcont are determined by the detected ratios R/B and B/G, respectively. Thus, gains of white balance control amplifiers can be controlled. Usually, illuminating light having color temperature 3200K is utilized as a reference illuminating light. A desired reference illuminating light having an optional color temperature can be obtained by using a color temperature convert filter with the reference illuminating light in order to approximate light of sunshine, an indoor fluorescent lamp and an incandescent lamp, so that a color temperature detecting region for judging an actual light source and a color temperature control region for selecting proper control values Rcont and Bcont corresponding to the actual light source (described after) can be determined.
However, in the feed forward control operation, characteristic of image pick-up elements such as a charge coupled device, for example, dispersion of integral color filters, is influenced to a dispersion of detected values. Such a dispersion of detected values is negatively influenced white balance control. The desired illuminating light does not always match real sunshine and real indoor fluorescent illumination light. Therefore, when an object is photographed under sunshine or fluorescent lamp, a color temperature detecting region and a color temperature control region become wrong in some cases.
To resolve the above problem, in a conventional method, a color signal photographed at an optional temperature is divided by a color signal photographed under a reference illuminating light as a reference value. However, in the conventional method, dispersion caused by image pick-up elements can not be sufficiently reduced.
As a compact and portable video camera integrated with a video tape recorder (herein after it is referred as "video camera"), it has been developed a video camera as shown in FIG. 2 has been developed. As shown in FIG. 2, an outer packaging case 02 of the video camera 01 has a flat thin wall along a direction from the front to the rear of a camera body (arrows A, B in FIG. 2) and a generally rectangular parallelpiped shape. A photographing lens 03 and an optical view finder 04 are mounted at an upper portion of the outer packaging case 02. A stereo microphone 05 is mounted on a top portion of the outer packaging case 02. Numerals 06, 07, and 0809 indicate a video tape recorder deck, a side grip portion, a photograph button and a telescope/wide switch button, respectively.
In the video camera 01 as shown in FIG. 2, an optical view finder 04 is utilized instead of an electronic view finder, so that an operator can find an object or a sight through the optical view finder 04 even if electric power is turned off. For such a video camera 01, a power save mode can be designed to an integrated circuit.
In the video camera 01 with a power save mode program, even if a power switch is shifted to ON and the photograph button 08 is not actuated, electric power is supplied to a part of mechanical portion and a microcomputer. However, electric power is not supplied to a computing mechanism part of the microcomputer and a circuit of a photographing mechanism part so that electric energy can be saved. During such a power save mode, a rotational drum can be rotated and a mechanism part of the microcomputer for detecting sensor signals and ON/OFF conditions of the photograph button 08 is operable. However, electric power is not supplied to a charge coupled device (CCD), an integrated circuit for processing image signals and the computing mechanism part of the microcomputer and the iris is closed. In the power save mode, a sight or an object can be seen through the optical view finder 04 by an operator.
While a power switch is shifted to ON and the photograph button 08 is being pushed, the power save mode is released electric power is supplied to all mechanical and electric mechanism parts, and a picture image is output from the charge coupled device. If the photograph button 08 is being pushed continuously after the power save mode is released, the iris is moved to open at high speed until an exposure value becomes a proper level. Then, recording is actually started at a moment (for example, 0.50 second) after pushing the photograph button 08. A reason why the start timing of actual recording is delayed from the moment of pushing the photograph button 08 is due to a delay of a mechanical action.
If recording is actually started, it is preferable to have a stable exposure value from an initial stage. Therefore, in a period I from pushing the photograph button 08 until actually recording (see FIG. 3), white balance control is calculated by picking up a picture image signal, values of white balance control singals are detected, the detected value are converged to some proper values (just computing without actual white balance control operation), and then computed white balance control signals are output at an initial stage of actual recording in order to control white balance. After the period I, that is, the open degree of the iris becomes stable, recording is started in the period II. However, regarding the period I for computing the values of the white balance control signals, it has to be remembered that the period I is very short and an open degree of the iris is remarkably changed, that is, a brightness level is rapidly changed.
Generally, in the case of controlling white balance control, color difference signals R-Y and B-Y are utilized for detecting signals. If the color difference signals R-Y and B-Y are used as the detecting signals, as shown in FIG. 4, brightness (brightness level) becomes an important factor. If the brightness level is increased, the levels of the color difference signals are increased. In FIG. 4, white small blocks indicate a color difference signal B-Y and black small blocks indicate a color difference signal R-Y. Therefore, even if the same object is photographed, values of the white balance control signals are different due to increasing color saturation simultaneously with increasing brightness level. Within the time period I (see FIG. 3), an open degree of an iris is changed and brightness level is rapidly increased. In addition, an iris meter is actuated at high speed, hunting is apt to occur and brightness level is unstable in this condition. Even if white balance control is computed based on the color signals R-Y and B-Y as detecting signals, the white balance control can not be operated accurately.
In a conventional white balance control, the reason why a period of the white balance control is long is because color temperature is not changed very much when photographing at the same place and it is not suitable to change the brightness level of a recorded picture image rapidly. For example, the white balance is controlled once for every 20 through 30 fields. However, the above described period I is very short so that a conventional slow computing method can not be utilized sufficiently.